Stereo cameras and millimeter-wave radars are commonly used as vehicle-mounted distance sensors. However, these devices have their own share of problems: the stereo camera loses its accuracy in dark places and at long distances, and the millimeter-wave radar has trouble dealing with multiple reflection in tunnels, for example, and has difficulty in acquiring information in the vertical direction.
Meanwhile, technologies have been disclosed which fuse the information obtained from these two types of distance sensors. The disclosed technologies are aimed at getting each of the two sensors to compensate for the conditions and ranges in which the other sensor is not strong.
For example, PTL 1 discloses technologies by which, if the distance information from the radar and that from the stereo camera are to be merged and if there is a long distance to an object, the confidence level of the radar-derived information is raised in order to increase the lateral position accuracy of the object. If there is a short distance to the object, the technologies involve raising the confidence level of the information from the stereo camera because there is no knowing how exactly the radio waves of the radar are reflected by the nearby object.
Further, PTL 2 states that the probabilities of the presence of a solid object obtained from the outputs of multiple sensors are corrected on the basis of the recognition rates of the sensors or are varied in a weighted manner depending on the traveling environment, before the probabilities are fused.
Further, PTL 3 discusses measures to be taken when the vehicle ahead being tracked by adaptive cruise control is off the range of detection of a millimeter-wave radar. Specifically, if the own vehicle is determined to be in a traffic intersection by a GPS (Global Positioning System), the confidence level of the millimeter-wave radar is lowered while the confidence level of a stereo camera is raised at the same time. The measures are intended to keep an appropriate distance between vehicles.